F1
Junkers Internal sensor / reference voltage fault

Boiler displays F1; sensor supply or internal sensor error

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Defective main PCB, Short circuit on sensor bus, Incorrect wiring modification, Moisture on PCB

How to Fix / Troubleshooting

Safety: Disconnect power before opening the boiler.

  • Visual inspection: Look for signs of water ingress or condensation inside the control compartment. Fix any leaks before further operation.
  • Drying: If moisture is present, allow the boiler to dry completely and then retry.
  • Technician checks:
    • Disconnect sensors one by one to identify a shorted component.
    • Measure reference voltages on the PCB according to Junkers service documentation.
    • Replace the main PCB if internal fault is confirmed.
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Repair Difficulty

Professional Required 5/5

Required Part

Main Control PCB
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